Many industries rely on fluids for lubrication, transport, pressure support, and other tasks. In some cases, a fluid may be relied on to perform more than one task at a time. For example, in oil and gas, geothermal and water drilling fluids help lubricate the drilling process, transport cuttings to the surface, reduce mixing with fluids (e.g. groundwater), and stabilize the wellbore. Drilling fluid (or drilling mud) often must be designed to perform these functions simultaneously.
A ready reserve of drilling fluid is required to add to the existing fluid as the wellbore is extended and to replace fluid that flows away from the wellbore. Significant amounts of fluid may be lost when the wellbore traverses fractured, permeable, or porous formations (loss formations or zones). In these cases, in addition to providing pressure support and transporting cuttings to the surface, the drilling fluid may be required to help stem the flow of fluid into the loss zone. In cases of significant loss, solids may be added to the drilling fluid to aid in blocking the flow of drilling fluid out of the wellbore and into the loss zone.
Drilling fluids commonly contain some materials or compounds that aid in creating a low permeability barrier on the walls of the wellbore. This is intended to prevent fluid from leaking out of the wellbore as well as external fluids from leaking into the wellbore. In the case of porous or fractured formations, the loss of fluid may be significant—sufficient to cause the wellbore to collapse. In these cases, additional materials may be required to prevent fluid loss. The added materials usually have a diameter that is similar in size or larger than the pore diameter (or the width of any openings such as fissures or fractures) of the formation being drilled. These materials are typically referred to as lost circulation materials, or LCMs. LCMs are usually inexpensive bulk additives that may be added to a wellbore, via the drilling fluid, in order to remediate fluid loss. Typical LCM's are in the form of flakes (or laminates), granules, or fibers (natural and synthetic). Where fissures, fractures, or voids have a large diameter, it may be difficult to remediate fluid loss with traditional LCMs, as their diameters may be too small to properly seal the fissures, fractures, or voids and prevent fluid loss from the wellbore. In these cases, it may be necessary to replace the drilling fluid with a cement mixture to stabilize the formation. However, this requires significant expenditures in both lost drilling time, specialized contractors and added materials. In some cases, when the drilling fluid cannot be properly replaced with a cement mixture, or is not replaced in sufficient time, the wellbore may collapse or be abandoned as unworkable.
Wellbores may require placement of temporary or permanent plugs or barriers. In some cases, wells are abandoned when they reach the end of their useful life, or where the wellbore is unproductive. In those instances, plugs are placed within the borehole to prevent migration of gas or fluids between the different formations and/or to the surface. Those plugs may be permanent or temporary. In addition, temporarily plugging a wellbore may be useful for the purpose of directional drilling and for sealing off formations. For directional drilling, a temporary plug is created in the wellbore to aid in creating the turn radius. In most cases, temporary plugs are designed so that they can be re-drilled later, if necessary.
Permanent plugs are useful where a wellbore is abandoned or where the operator wishes to prevent further use of the wellbore. Regulations in some jurisdictions may require plugging wells before they are abandoned. In the U.S., plugging and abandonment regulations vary between states, but numerous unplugged wells exist today. In most cases, cement is used to plug wells.
Expansive mortars are calcium-containing fluid compositions that may be used in place of explosive or mechanical methods for demolition and detachment of rock. Expansive mortars are created by mixing water with an expansive powder, which includes calcium oxide and various other oxides. Expansive powders may also include various carbonates, and/or salts. Immediately after mixing, expansive mortars are fluid, allowing them to be poured into holes created (or existing) in the target rock or structure. In most embodiments, expansive mortars are slow-acting, but exert significant force. However, because of the fluidity of expansive mortars, they are generally restricted to applications where holes are vertical, or the hole can be physically plugged to prevent the fluid mortar from leaking out.